How to Fit a New Lead Roof

How to Fit a New Lead Roof

New Lead bay roof

A very hard roof to better, lead roofs have been around for hundreds of years with very little need for change. If laid correctly and the correct Code (thickness) it is not uncommon for a lead roof to see 50 – 100 years without replacement. A new lead roof finished with Patination oil is a timeless classic, unfortunately these days they are prone to being stolen for scrap if easily accessible from the floor.

Lead Code explained

Lead code is a way of combining thickness and weight, very handy to know if you’re thinking about lifting it off your van and onto a roof. Lead for the purpose fitting to a roof or bay window really starts at Code 4 in theory, if the roof is small enough you could use Code 3 but this would normally be classed as a flashing lead i.e. small over flashings or leak soakers. As a rule of thumb the larger the size of the roof the thicker the lead needs to be to avoid premature failure due to fatigue cracks.

Lead codes chart – Here is a simple chart of milled lead sheet, lead code, lead weight and thickness.

How thick should my lead be?

This is a good question without a straightforward answer, If you think about things logically the larger the roof or square metre-age the thicker the lead should be. If for instance we took things to extremes, on a roof the size of a postage stamp Code 3 would seem thick, in fact it would last so long that the rain would have to physically wear it away. On the other hand the same lead stretched over a football field would expand and contract so much with heat and cold that fatigue cracks would finish it off in no time.

Now there’s a lot of lead snobbery among builders and roofers who will say a certain size roof ‘needs code 5 or 6, 7, 8, but the truth is you have to balance out the size and required lifespan, ie. do you need it to last 100 years? would 25 years suffice? All situations and budgets are different.

Suggested Lead size and thickness

If money was no object it would be Code 8 and triple brandy’s all round, but its not so whilst technically Code 3 is a flashing lead, and it can be fitted to small bays and lead roofs in the right circumstances. I know because I’ve done it, and I’m still driving past jobs I’ve done 30 Years ago and guess what? No problems. In fact I can’t believe how good they still look myself, so I’ll try to give you some sizes that I think will match up with a certain code but pushed to the limit, so feel free to up the code if you like.

Code 3 – 2.5m2 maximum

Code 4 – 4m2 maximum

Code 5 – 5m2 maximum

When we get to Codes 6,7 and 8 make sure you can physically get the lead onto the roof if it’s a large piece. Obviously if it’s your choice, it’s your money so you choose. I always give my customers a choice of code, as long as I know it will not fail them prematurely.

Shape and size of roof

Another factor to consider is the shape of your lead roof, the longer and thinner it is the thicker and therefore higher Code you should go. Fairly logical stuff eh?

How to replace a Lead Bay Roof

After you’ve removed the old lead or felt sweep of the dirt and oxidised lead, remembering to be up wind and wearing a mask, check thoroughly for loose boards. I would recommend screwing them down to avoid any heavy banging on the plastered ceiling beneath. Finally check for old nails or Sharp objects poking up and tap them in if necessary.

What drip size on a lead bay roof ?

Lead drip – The edges of a lead bay roof are called the ‘drip. When determining the correct size it pays to look around and see what is in keeping with your neighbour’s properties. Keep in mind too big and they are liable to catch any wind gusts, too small and the drip will not drip the water clear of any wood or paintwork as it should. Most of my drips are around 40mm mark.

Membrane under lead

Breather membrane – Roofing membrane is becoming more commonplace these days. By placing some breathable roofing membrane over the roof first, apart from anything else, it can help the lead move. Always check any old wood for nails poking up and knock them in.

How to Install a new lead roof Fixing lead

This needs serious consideration, the more nails you put in the lead the less it can move to accommodate expansion and contraction and the faster you will kill off your nice new roof, less is more. Just enough so it doesn’t blow off in a wind and no more. If you can fix it with lead straps or by beating the edges tight over the wooden drips or mopsticks this will often suffice without pumping the edges full of nails. Some builders and roofers use a few beads of P.U. Adhesive around the edges.

A new lead bay fitted – In a simple one piece bay like this one, the lead is nailed into the upstand underneath the guttering.The drip is then beaten nice and tight over the edge of the roof and trimmed to about 50mm. Note, no nails in the edge.

Lead mopsticks

Used to join lead together into smaller pieces, reduce expansion and contraction issues, create up-stands and troughs, provide fixing points and decorative interest.

A mop stick – The mopstick is a piece of round wood like a fat broom handle with one flat edge to fit face down onto the roof, the purpose of which is to separate one section of lead from another whilst providing an up stand.

Separator – Used to separate two sections of roof, a mopstick also allows you something to fix nails into and fold the other cloaking piece of lead over the top to conceal the fixings. Notice the 450 to 60o angle cut on the edge of the mopstick to provide a pleasing look and make lead dressing easier.

Mopstick done – An example of mopsticks being used over a Dormer roof. Mopstick details are used in roofing for bay windows also.

Angle Fillet or Firing strips used in roofing for bay windows

These can be very useful to avoid lead soldering, complicated folds and beating the lead too thin when dressing the rear of a two piece or more bay window. Fitted to the back of the roof where it touches a wall or upstand, it removes the need to tightly beat into the corner of a mopstick and wall, this creates a nice gentle flow away for the join.

Mopstick under lead – This picture shows what can is hidden underneath the visible lead. The mop stick creates the join, and the angle fillet provides a nice smooth transition between upstand and roof deck.

Final finish – This is all that is visible on the exterior of the roof. The lead apron flashing is chased into the brickwork underneath the render to finish, and onto the upstand of the lead bay roof.

How long should my lead flashings be ?

See my guide on how to fit apron flashings like these in the page links below…

Flashing – If you need to install lead cover flashing either into the brickwork above a bay, or underneath the roof against a fascia, do not use a continuous length. When fitting lead flashings I tend to use about 1 metre or 3 feet lengths to allow for expansion and contraction up to a maximum of 1.5 metres then overlap any joints by 100mm minimum (4″)

Patination Oil the finishing touch

Developed for the Lead Sheet industry, Patination Oil is a white spirit based liquid that helps prevent white carbonate or oxidisation (that can occur on newly fitted Lead) from staining adjacent materials and provides a pleasing finish to new Leadwork.

Patination oil – Ideal for use on Lead roofing, flashings and cladding to give a uniform, attractive appearance where Lead sheet is visible or where water flowing away from the lead sheets surface may come into contact with other visible building materials like brickwork, tiles or fascia’s.